As a user, I found almost all of the changes made to sites like I once used (like the main page or flickr, or the finance page) to be worse than before she was there.
She did some very bad hires such as Henrique de Castro who in 15 months got over 100 million in salary, stock and severance.
She wasted billions on acquisitions that did not add value.
The comments from Yahoo employees since she was hired were never very good, and her behavior with employees was said to sometimes be somewhat bizarre (such as reading a children's book at a comm meeting)
I agree that she likely never had a real chance at fixing the company, but I don't think that proves that no one couldn't have improved the company.
The yahoo brand no longer exists. I think if you randomly choose someone on hn they could have at least saved the brand name.
I much prefer to go in with the mindset that she tried her best but the situation was unwinnable.